A conventional gas turbine includes a rotor with various rotor blades and turbine buckets mounted to discs in the compressor and turbine sections thereof. Each blade or bucket includes an airfoil over which pressurized air or fluid flows, and a platform at the base of the airfoil that defines the radially inner boundary for the air or fluid flow. The blades and buckets are typically removable, and therefore include a suitable root, such as a T-type root, configured to engage a complementary attachment slot in the perimeter of the disc. The roots may either be axial-entry roots or circumferential-entry roots that engage corresponding axial or circumferential slots formed in the disc perimeter. A typical root includes a neck of minimum cross sectional area and protrusions extending from the root into a pair of lateral recesses located within the attachment slot.
For circumferential roots, a single attachment slot is formed between forward and aft continuous circumferential posts and extends circumferentially around the entire perimeter of the disc. The cross-sectional shape of the circumferential attachment slot includes lateral recesses defined by forward and aft rotor disc posts that cooperate with the root protrusions to radially retain the individual blades or buckets against centrifugal force during turbine operation.
In the compressor section of a gas turbine, for example, rotor blades (specifically the root component) are inserted into and around the circumferential slot and rotated approximately ninety degrees to bring the root protrusions into contact with the lateral recesses to define a complete stage of rotor blades around the circumference of the rotor discs. The blades include platforms at the airfoil base that may be in abutting engagement around the slot. In other embodiments, spacers may be installed in the circumferential slot between adjacent compressor blade platforms. Once all of the blades (and spacers) have been installed, a final remaining space(s) in the slot is typically filled with a specifically designed spacer assembly, as generally known in the art.
A common technique used to facilitate the insertion of the final spacer assembly into the circumferential slot is to include a non-axi symmetric loading slot in the rotor disc. However, loading slots are costly to manufacture and the inclusion of such a slot creates a location of high stress. Various conventional spacer assemblies have been designed to eliminate the need for a loading slot in a rotor disc but include complicated multi-component devices. These conventional assemblies are generally difficult to assemble, and are prone to coming apart during operation of the turbine, for example, if either side of the device develops clearance relative to adjacent components (i.e., the rotor discs or platforms). Accordingly, there is a need for a final spacer assembly that it relatively easy to assemble within the final space between platforms of adjacent airfoils of rotor blades or turbine buckets located within a circumferential entry attachment slot.